The microwave test method of space reflective wave was applied to study the attenuation characteristics of differently polarized wave scattered by microwave argon plasma jet in vacuum and its influencing factors. Experimental results show that in the 4—8GHz frequency area of testing wave, the plasma absorbs vertically and horizontally polarized wave obviously. The mass flow rate and power of generator and the background pressure affect the attenuation of vertically polarized wave. But the power of generator and degree of vacuum almost do not affect the horizontally polarized wave attenuation.